Porous membranes are widely used in the filtration of particulate, ionic, microbial and other contaminants from fluids in pharmaceutical, microelectronics, chemical and food industries. In use, the membranes are formed into a device (e.g., pleated cartridges which may be housed within a capsule, hollow tubes, stack of flat disks, etc.) which is placed in the fluid stream to be filtered.
To meet chemical and temperature resistance requirements, most filtration devices used in semiconductor fabrication are constructed entirely of fluoropolymer materials. The trend towards narrower line widths in semiconductor manufacturing has placed an ever increasing burden on particulate contamination control in semiconductor fabrication. Such a trend has led to the introduction of fluoropolymer filtration membranes having rated pore sizes as low as 10 nm.
While such membranes provide superior particle filtration, there is a desire to extend the life cycle, or time-in-use, of the membranes, while maintaining the filtration efficiency thereof. In this regard, in typical filtration implementations, a support layer may be positioned downstream of a fluoropolymer filtration membrane to support the membrane against the pressure of fluid flow. In addition, the support layer or another downstream layer may provide drainage functionality (e.g., by acting as a spacing layer with downstream passageways therethrough to thereby facilitate fluid flow through the membrane). In that regard, an upstream drainage layer may also be utilized.
In such arrangements, known upstream and downstream layers are constructed of fluoropolymeric fiber materials (e.g., PTFE, PFA or PVDF) in the form of wovens, non-wovens or nets. Over extended periods, such woven, non-woven or net layers may exhibit movement of fibers in the layer structure to a degree that renders such layers unable to provide the desired support to the filtration membrane against applied fluid pressure. This may result in damage to the membrane microstructure, and degradation of filtration efficiency and drainage functionality, to the point that filter replacement is required. As may be appreciated, filter replacement entails not only system downtime, but also results in added filter costs and utilization of maintenance personnel resources.
Therefore, a need exists for a fluid filtration article having extended time-in-use advantages, while providing satisfactory filtration efficiency over the extended life of the device. Fluid filtration articles constructed with the knit materials of the present invention fulfill such a need.